1. Field of the Invention
This invention relates to a CDMA (code division multiple access) communication apparatus usable in a communication system such as a mobile communication system or a wire communication system.
2. Description of the Prior Art
In a typical CDMA communication system, a base station can communicate with mobile stations to which different pseudo-noise codes (spread codes) are assigned respectively. In the base station, base-band information pieces to be transmitted to the mobile stations are modulated in response to the pseudo-noise codes respectively, before being combined and multiplexed into a composite information signal. Then, a carrier is modulated in response to the composite information signal. The base station transmits the resultant modulated carrier toward the mobile stations via a downlink. Each of the mobile stations receives the modulated carrier. At each of the mobile stations, the composite information signal is recovered from the received carrier, and then the composite information signal is demodulated into the related base-band information piece in response to the assigned pseudo-noise code.
Generally, the base station is provided with a transmission de-correlator for processing pseudo-noise coded information to prevent or eliminate interferences between communication channels in the downlink. As will be described later, a prior-art transmission de-correlator tends to be complicated in structure.